Principal faults in the Green Lake Arch Dam region were examined and an assessment was made of potentially damaging earthquakes. An earthquake which can cause the most severe ground motion at the site (Maximum Credible Earthquake) and another one which has a recurrence interval of 100 yr, were selected for use in design. A dynamic analysis using the time-history method was performed, showing that vertical contraction joints would partially open for short instants under dynamic loading. It was concluded that the dam can resist the Maximum Credible Earthquake without an uncontrolled release of water from the reservoir, and that the dam can withstand the 100-yr earthquake with little or no damage.